Light Guiding Unit Prism Geometry for End Illuminance
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Solution Overview
Problem
The end portion arrangement-type light illuminating devices in image reading apparatuses face challenges in enhancing illuminance near the end surface and suppressing shadows of three-dimensional objects due to the optical path length and angle of light beams, which are not effectively addressed by existing solutions that require extending the light guiding member or precise alignment of reflective surfaces.
Innovation Solution
A light guiding unit with a light guiding member and a diffusion member, where the light guiding member has a plurality of rectangular prisms arrayed on its surface, satisfying the condition W tan(sin−1(1/n))≦H≦2W, to efficiently guide light and reduce shadows without increasing the longitudinal length of the light guiding member or requiring high positional accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the light guiding member is extended in the main scanning direction to improve illuminance distribution, then the illuminance near the end surface is enhanced, but the longitudinal length of the light guiding member increases causing apparatus upsizing
Solution Approach 1:
The invention applies local quality by forming prisms only at specific locations (second and third side surfaces) of the light guiding member rather than uniformly across all surfaces. This localized structural modification changes the light guiding properties only where needed, improving illuminance distribution near the end surface without requiring extension of the entire light guiding member length.
Solution Approach 2:
The invention transitions from modifying the light guiding member in the longitudinal dimension (extension) to modifying it in the transverse dimension by adding prism structures on side surfaces. This dimensional shift allows achieving better illuminance distribution through surface geometry modification rather than lengthening the member.
2Illumination intensity
If the diffusion surface is formed with saw-like triangular prism or trapezoidal prism shape to guide light, then light propagation is improved, but the angle of light beam causes separation from end surface reducing illuminance enhancement
Solution Approach 1:
The invention uses different surface configurations at different locations: flat or diffusion surfaces at the first side surface, and prism structures at the second and third side surfaces. This localized differentiation allows each surface to perform its specific function optimally without interfering with others, improving overall light guidance while maintaining manufacturability.
Solution Approach 2:
The light guiding member's surface is segmented into different functional zones: the first side surface with diffusion characteristics, and the second and third side surfaces with prism structures. This segmentation allows independent optimization of each surface's light guiding properties, achieving better overall performance.
3Object-affected harmful factors
If a reflective plate with concavo-convex shape is arranged to suppress shadows, then shadow suppression is improved, but high positional accuracy between light guiding member and reflective plate is required
Solution Approach 1:
The invention merges the shadow suppression function directly into the light guiding member by forming prism structures on its side surfaces. This integration eliminates the need for a separate reflective plate, thereby removing the requirement for high positional accuracy between two components while still achieving effective shadow suppression.
Solution Approach 2:
The invention extracts the shadow suppression function from the separate reflective plate and incorporates it into the light guiding member itself through prism structures. This extraction eliminates the dependency on precise alignment between separate components.
4Illumination intensity
If multiple LEDs are arranged in array configuration to enhance illuminance, then illuminance distribution is improved, but the usage number of LEDs increases causing device complexity
Solution Approach 1:
The invention replaces the mechanical approach of using multiple LED components with an optical approach using prism structures on the light guiding member. This substitution achieves improved illuminance distribution through optical path modification rather than increasing the number of light source components.
Solution Approach 2:
The light guiding member is given multiple functions: it guides light from the LED and simultaneously modifies light distribution through its prism structures. This multi-functionality allows a single component to achieve what would otherwise require multiple components, reducing device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances illuminance near the end surface and suppresses shadows of three-dimensional objects, achieving a sufficient longitudinal illuminance distribution while maintaining a compact device size and avoiding the need for precise alignment.
Implementation Method 1
light entering the light guiding member from the incident surface is guided via the light guiding surface to the exit surface
Implementation Method 2
a diffusion member opposed to the light guiding surface, in which: light entering the light guiding member from the incident surface is guided via the light guiding surface and the diffusion member to the exit surface
Data Source
AI summary
Provided is a light guiding unit including: a light guiding member including an incident surface, an exit surface elongated in a first direction, and a light guiding surface opposed to exit surface; and a diffusion member opposed to light guiding surface, in which: light entering the light guiding member from incident surface is guided via light guiding surface and diffusion member to exit surface, and exits from exit surface to illuminate the original; the light guiding member further includes a plurality of prisms arrayed in first direction on light guiding surface on a side opposed to diffusion member; each of prisms has a rectangular shape in a first section; and each of prisms satisfies the following condition: W tan(sin−1(1/n))≦H≦2W, where W and H represent a width and a height of each of prisms in the first section, respectively, and n represents a refractive index of the light guiding member.